The implementation of roundl for ldbl-128 involves undefined behavior for arguments with exponents from 31 to 47 inclusive, from the shift:
u_int64_t i = -1ULL >> (j0 - 48);
For example, on mips64, this means roundl (0xffffffffffff.8p0L) wrongly returns its argument, which is not an integer.
This is GCC libquadmath bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65757 .
Working on a patch.

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=7d0b2575416aec2717e8665287d0ab77826a0ade
commit 7d0b2575416aec2717e8665287d0ab77826a0ade
Author: Joseph Myers <joseph@codesourcery.com>
Date: Tue Apr 28 17:27:02 2015 +0000
Fix ldbl-128 roundl for exponents in [31, 47] (bug 18346).
The implementation of roundl for ldbl-128 involves undefined behavior
for arguments with exponents from 31 to 47 inclusive, from the shift:
u_int64_t i = -1ULL >> (j0 - 48);
For example, on mips64, this means roundl (0xffffffffffff.8p0L)
wrongly returns its argument, which is not an integer. A condition
checking for exponents < 31 should actually be checking for exponents
< 48, and this patch makes it do so. (That condition is for whether
the bit representing 0.5 is in the high 64-bit half of the
floating-point number. The value 31 might have arisen from an
incorrect conversion of the ldbl-96 version to handle ldbl-128.)
This was originally reported as a GCC libquadmath bug
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65757>.
Tested for mips64; also tested for x86_64 and x86 to make sure the new
tests pass there.
[BZ #18346]
* sysdeps/ieee754/ldbl-128/s_roundl.c (__roundl): Handle all
exponents less than 48 as cases where high part of mantissa needs
examining to determine whether argument is integral.
* math/libm-test.inc (round_test_data): Add more tests.
-----------------------------------------------------------------------
Summary of changes:
ChangeLog | 8 ++++++++
NEWS | 2 +-
math/libm-test.inc | 11 +++++++++++
sysdeps/ieee754/ldbl-128/s_roundl.c | 2 +-
4 files changed, 21 insertions(+), 2 deletions(-)